1. Field of the Invention
The subject invention generally pertains to plenum fans and more specifically to an inlet cone arrangement for such a fan.
2. Description of Related Art
A typical plenum fan comprises a fan wheel inside a plenum of a box-like enclosure. Upon drawing air into the enclosure through an inlet, the fan wheel pressurizes the air in the plenum. An outlet in the enclosure releases the pressurized air to perhaps a supply air duct, which can convey the air to a comfort zone or to wherever the air is needed.
To promote smooth inlet airflow, many fans include some type of inlet cone. Examples of various inlet cones are disclosed in U.S. Pat. Nos. 2,798,658; 2,798,659; 3,070,287; 3,278,115; 5,525,036 and 5,551,838. For efficient operation, it usually helps to align such inlet cones accurately to the inlet mouth of the fan wheel. Such alignment can be difficult to maintain if the fan wheel vibrates or otherwise translates relative to the inlet cone. If the radial and axial position of the inlet cone is fixed relative to the fan wheel, then the two might vibrate as a unit. If the vibration transmits to the enclosure of a plenum fan, the enclosure's relatively large side panels might emit appreciable noise. Although plenum fans can be provided with various vibration dampening devices, such devices might adversely affect an inlet cone's alignment to a fan wheel, or they might disrupt an otherwise smooth inlet airflow pattern. Consequently, a need exists for a plenum fan with smooth, quiet and efficient operation.